1. Field of the Invention
This invention relates to the art of closures for ladles of the type used for carrying molten metal, including ladle cars and, more particularly, to a new and improved disposable cover for closing the opening of a preheated ladle car for retaining the heat therein after heating and before pouring molten metal therein.
2. Description of the Prior Art
The present invention finds its primary use with ladle cars, also called torpedo cars from their shape, transfer cars from their function, and Pugh ladles after their originator (U.S. Pat. No. 1,488,436). Such ladles are used in steel mills and like plants for moving molten metal from one location to another, for example, from a blast furnace to a continuous caster. U.S. Pat. No. 3,661,374 depicts one such ladle car. The cars have an opening and are conventionally rotatable along their long axis for discharging metal from the opening. Such cars, as is the case with conventional ladles for molten metal, are lined with a refractory material. To prevent damage to this material when the extremely hot molten metal is poured into the ladle, the ladle is conventionally preheated. This is often done by inserting gas burners into the opening of a partially rotated ladle and heating the interior over a period of time to raise the lining temperature.
Now it often occurs that the heating station for the ladle is located a good distance from the source of metal or that because of scheduling delays or convenience in use, the car may have to wait a period of time before it is used. While permanent covers for ladles (e.g., U.S. Pat. No. 1,488,026) and Pugh ladles (U.S. Pat. No. 4,298,191) have been suggested, in practice, it is more efficient to prevent the waste of heat and, more importantly, the lowering of the lining termperature by using disposable lids or plugs.
Such coverings can also be used to cover molten metal containing ladles to prevent heat loss from the metal during transfer. In use, molten metal is poured through such coverings (melting upon contact the coverings and chicken wire).
A third and major use of such a covering is to conserve heat and maintain the temperature of a ladle after it has discharged its load of molten metal and while it is being returned for a second load.
It has been the practice to use ceramic batting reinforced in one or both sides with chicken wire. In one common form, this takes the shape of an oval or rectangular blanket that is laid over the mouth or opening of the ladle car. Such oval blankets are stored and shipped folded over in a half-moon shape.
In use, these blankets tend to sag or deform as the chicken wire stretches and softens as its temperature rises, tending to form an opening or openings through the blanket. Also, the lightweight blanket tends to blow off, partially or wholly, when subjected to gusts of winds often present in and around steel mills, especially when the car is being moved about, e.g., from the preheating station to a blast furnace. Thus, openings tend to form, resulting in a loss of heat.
It has also been suggested in U.S. Pat. No. 4,390,170 entitled Closure Plug for Ladle Car to form the chicken wire blanket into a conical shape that plugs the opening more or less like a cork in a bottle.
However, this construction would also tend to sag, especially as the chicken wire is placed on the underside of the plug. When used as described over ladle cars filled with molten metal, there is the possibility of having the plug bottom dissolved by contacting the molten metal.
One disadvantage of such prior closures is the difficulty of handling, storing, and transporting them. The typical blanket may be about 6.times.10 feet in size and even when folded over is a 6.times.5 foot unit. The conical shape suggested by the above-mentioned patent, while perhaps stackable in a nested array, would still be bulky and difficult to store, ship, and handle. Further, the ceramic batting of the insulation is relatively fragile and easily torn by contact with sharp edges or points during storage and handling. Thus, bulkiness in storage and difficulty in handling are significant disadvantages. Further, the chicken wire surface tends to "grab" or snag easily, making handling, as well as stacking or nesting, difficult.
Also, the unprotected insulation of prior covers while relatively non-absorbent of moisture, if exposed to rain or other sources of water during storage or handling, can entrap water droplets. This liquid when exposed to the high heat as when the cover is placed over a hot ladle can flash into steam with resulting damage to the insulation. Moisture can also cause the cover to deteriorate while in storage.